1. Field of the Invention
The present invention generally relates to the field of data processing and systems and methods for data processing. More particularly, and without limitation, the invention relates to data models and query processing.
2. Background Information
Data models, such as entity-relationship-models, are commonly used for database design. A data model is a conceptual description of data objects, i.e., entity types, their attributes, and the relationships between them. There are different types of data models, depending on the data structures to be defined, such as a relational data model.
ACM Transactions on Database Systems, Volume 1, No. 1, March 1976, Peter Pin-Shan Chen “The Entity-Relationship Model—Toward a Unified View of Data”, pages 9-36 shows a data model. This model incorporates some of the important semantic information about the real world serving as a tool for database design.
From U.S. Pat. No. 4,479,196, to Ferrer et al., a diagrammatic technique to represent an entity relationship model is known for usage in a database system. This technique is directed to represent databases in a form that is readily processed and efficiently utilized by digital computers.
Large applications can be based on very complex data models. Searches are usually performed by using structured query language (SQL) expressions. For more information on the use of structured query language, see “A Guide to SQL”, Philip J. Pratt, Boyd & Fraser Pub Co, February 1995, ISBN: 0877095205. Search expressions may be quite complex and their results may be relied upon to produce appropriate reports within the database application.
The data of a data model can be stored on a single data processing system or it can be stored on various distributed internal and/or external data sources. A disadvantage of distributed data processing in which various kinds of internal and/or external data sources are relied on is that each individual data source may require a dedicated interface. This makes prior art distributed data processing systems difficult and costly to implement. A further disadvantage is a lack of flexibility and high maintenance costs.